I cant use l'Hôpital's rule

1. Nov 29, 2011

asi123

1. The problem statement, all variables and given/known data

Hey guys.

Can I please have some help with this limit over here

http://imageshack.us/photo/my-images/839/targil.jpg/

BTW

I cant use l'Hôpital's rule.

I'm trying to help someone how haven't learned how to Derivative yet.

Thanks a lot.

2. Relevant equations

3. The attempt at a solution

2. Nov 29, 2011

ehild

Re: Limit

Multiply both the numerator and denominator with
$$(\sqrt{x^2+1}+1)(\sqrt{x^2+16}+4)$$ and simplify.

ehild

3. Nov 29, 2011

asi123

Re: Limit

It will switch between the numerator and the denominator and will change the sign of the 1 and 4.

How can that help?

Thanks a lot.

4. Nov 29, 2011

asi123

Re: Limit

Ops, that's the solution.

Thanks a lot.

5. Nov 29, 2011

ehild

Re: Limit

You are welcome. And remember the method, it is always useful when you have difference including square root(s)

ehild